This is coming from the CSS rules. For example:
.weglot-flags span:before{/*...*/background-image:url("../images/rect_mate.png");/*...*/}
And:
.wgcurrent:after{/*...*/background:url("../images/wgarrowdown.png") no-repeat;/*...*/}
The plugin adding these style rules needs to use absolute paths instead of relative ones (e.g. ../
).